<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    /*
    p{}元素选择器
    */
    .one{
        color: red;
    }
    .two{
        color: green;
    }
    .three{
        color: blue;
    }
    .bg{
        background-color: black;
    }
    
    </style>
</head>
<body>
   <p>hello world</p> 
   <p class="one">hello world</p> 
   <p class="two">hello world</p> 
   <p class="three bg">hello world</p> 
   <p>hello world</p> 
   <p>hello world</p> 
</body>
</html>